Hi Dom,
Thank you for posting us here in Microsoft Community! We will need the following information for us isolate your concern.
When was the last time are you able to use the microphone on your Surface Headphone?
Were there any changes made before you get to this issue?
Is this happen to all application? If not, what specific application having this issue?
For the meantime, you try the following steps that may help fix your concern.
- Try to check the app settings if there's an audio input settings that can be configured to use Surface Headphone.
- Try to close the application that’s being used as the audio source on the host device, and then open it again.
- Restart the host device.
On Windows, selectWindows, selectPower, then select Restart*(not Shut down).*
On Android, hold down the power button until you see options to turn off your device, and then selectRestart.
On Apple iOS, hold down the power button until you see the slider to turn off your device, and then move the slider to turn off. After the device turns off, press the power button to turn it back on.
- Check to see if there’s a firmware update available via the app.
Cortana Device Setup app (Windows – US only)
Cortana App (iOS/Android – US only)
Surface Headphones app (UK)
For more information, see Update Surface Headphones
- Reset the headphones back to factory settings.
First, press and hold the power button for about15 seconds, until you hear that your headphones have been reset to the factory defaults. You will then hear “You’re ready to pair,” and the headphones will be in pairing mode. then pair the headphones to the host device by using the app.
For more information, see Reset Surface Headphones.
Keep us posted so we can assist you further,